The candidate is an academic neurosurgeon (MD, PhD), with a career scientific goal of understanding the molecular mechanisms of brain development and the pathological deregulation of those mechanisms in neurological diseases. The candidate has significant prior laboratory experience with a track record of successful, published research projects in developmental and excitotoxic neuronal death and neuronal morphogenesis. To prepare for the transition to successful independent investigator, the candidate's career development plan includes graduate-level coursework in bioinformatics, next-generation sequencing, and genomic analysis, as well as academic medical leadership and will be supplemented with seminars in Genetics, Anatomy and Neurobiology, and the Hope Center for Neurological Disorders, as well as presentation of the candidate's research at major national and international conferences. The proposed career development plan and scientific training will occur at Washington University in St. Louis, an institution with particular strengthsin neurobiology, genetics, and advanced genomic approaches, providing the candidate with important intellectual assistance and collaborations. The scientific training will be mentored by Dr. Jeff Milbrandt, whose laboratory focuses on elucidating mechanisms of gene regulation during nervous system development. His laboratory's expertise in the latest transgenic mouse technology, transcriptome analyses, and methodologies to study protein-DNA interactions, as well as his knowledge of cohesion biology will provide the candidate with the research tools needed to succeed as an independent investigator studying neuronal development and diseases that affect the human brain. Disturbances in neuronal dendrite morphology have been observed in diverse neurological disorders, raising the intriguing hypothesis that abnormalities in normal dendrite development contribute to human brain diseases. The candidate previously discovered that strikingly, major mitotic ubiquitin ligase Cdc20-Anaphase- Promoting Complex (Cdc20-APC) is required for dendrite morphogenesis in post-mitotic neurons of the brain. This research proposal will identify novel molecular mechanisms downstream of Cdc20-APC in the control of dendrite development, with direct relevance to human brain diseases. The first aim will define an exciting link between Cdc20-APC and the S5a subunit of the 26S proteasome, a multisubunit complex designed to destroy ubiquitinated substrates, in dendrite morphogenesis, suggesting the hypothesis that Cdc20-APC regulates proteasomal activity to drive dendrite elaboration. These experiments will use a rigorous RNA interference- based approach to determine the mechanism of S5a-driven dendrite morphogenesis and utilize a novel cellular fluorescent reporter to monitor Cdc20-APC regulation of proteasomal activity. The second aim will elucidate a Cdc20-APC signaling pathway to the cohesion complex in dendrite and dendritic spine morphogenesis. Human cohesinopathy syndromes are linked to mutations in cohesion genes and are characterized by mental retardation. This aim will test the hypothesis that dysregulation of a Cdc20-APC/cohesion dendrite morphogenesis pathway causes structural abnormalities in neurons, which may underlie the cognitive deficits seen in cohesinopathy patients. RNAi targeting the Cdc20-APC/cohesion pathway and transgenic mice carrying a conditional deletion of a core cohesion subunit will be extensively utilized for this aim. Direct downstream gene targets of cohesion in post-mitotic neurons will be identified through a genome-wide search for cohesion binding sites through chromatin immunoprecipitation coupled with next generation sequencing and correlated cohesion- dependent microarray analyses. The identification of novel Cdc20-APC downstream mechanisms in the control of dendrite morphogenesis will fill a significant gap in our understanding of cell-intrinsic mechanisms of neuronal connectivity and provide insights into the pathogenesis of the cognitive deficits observed in human cohesinopathies.